1. Field of the Invention
The present invention generally relates to computer local area networks, and more particularly to node devices having Media Dependent Interfaces (MDI) that are installed in such networks and their automatic connection configuration
2. Description of the Related Art
Many local area network products (LAN) use a medium consisting of twisted copper wire pairs for the transmission and reception of data. It is generally a requirement that one or more pairs be used for transmission of data in one direction and one or more other pairs to receive data in the opposite direction. The connection between two node devices is a link. For LAN technologies which employ a full-duplex medium, many have different pairs for transmission than for reception and thereby require that each end of the link use a defined assignment for its twisted pair connector to a particular pair of wires. For example, a Network Interface Card (NIC) is usually employed as an end node device, while a switch or a repeater will be employed as a concentrator or central component in a star-based network. For the link to operate, the NIC must transmit on a pair of wires that is connected to the receiver of the hub or switch and the NIC's receiver must be connected to the transmitter at the other end of the link. If the transmit pair of wires of a device are connected to the transmit connectors of the connected device, the communication link will obviously fail.
Most LAN standards address this by assigning different connector pins to the wires in the twisted pair which is typically referred to as the Media Dependent Interface (MDI). In the IEEE-802.3's 10BASE-T standard, an end node will assign pins 1 and 2 to the transmit pair while pins 3 and 6 are for connection to a twisted pair for receiving. The hub, which is typically a repeater or a switch for a 10BASE-T network, will assign its transmitter to pins 3 and 6 while its receiver will be connected to pins 1 and 2. This works quite well for configurations where NIC's are attached to repeaters, but there are a few cases that become more important to consider with the emergence of switched networks. First there is a case where the NIC is connected directly to another NIC, or a repeater is connected to a repeater or a repeater is connected to a switch. Depending upon the assignment of pins at the network interface, it may become necessary to employ a crossover cable to address the fact that both products employ the same pin designations on their interfaces.
Some products will use a manual "MDIX" switch, with MDIX being a hub, repeater or switch configuration as opposed to an end node device, which is known as a MDI configured device. The switch allows the products to connect to other similar devices but requires an installer to manually push a button. The approach worked well for limited applications like a repeater-to-repeater port, but not in the general case where it is desired to build a product that attaches to either a repeater, NIC or switch without manual intervention.
This resulted in the development of bus switches for making a solid state version of a crossover type circuit that used a low frequency alternating pin selection to perform an automatic operation. However, the product had the drawback that if two such devices were attached together, they could potentially get into a "lock step" operation where the necessary connections for establishing a communication link became impossible. Subsequently other products were developed which employed a similar algorithm and were forced to use a different alternation rate to avoid the lock step phenomena. While that worked for a limited set of products, it did not solve the general case whereby a guaranteed connection between nodes was achieved regardless of the manufacture or the model of product that was being used.